During some conditions, turbocharged direct-injection engines may generate increased soot. For example, during some conditions, fuel may not sufficiently mix with air before combustion, for example due to reduced turbulence. Such phenomena may occur when the engine is operating at high speed and/or high loads.
The inventors herein have recognized that one approach to address such an issue may be to utilize a particulate filter in the exhaust. However, regeneration of the filter in the exhaust of a spark-ignited engine aimed at stoichoimetric emission control raises numerous issues. As just an example, sufficient excess oxygen for regeneration in the exhaust may result in increased NOx emissions.
The present description addresses various aspects of such regeneration and associated control, including adjusting operation during and/or after an engine shutdown to enable regeneration under such conditions. Specifically, in one example, methods and systems for controlling regeneration of a particulate filter downstream of an engine coupled to an energy conversion device are provided. An exemplary method includes, during first engine shutdown conditions, increasing excess oxygen to the particulate filter by spinning the engine with the energy conversion device, and regenerating the particulate filter. The method also includes, during second engine shutdown conditions, decreasing the excess oxygen to the particulate filter.
By spinning the engine via the energy conversion device during engine shutdown, excess oxygen can be directed to the particulate filter so that the particulate filter can be regenerated, while reducing disturbance to the conversion of combustion exhaust emissions. Further, vehicle motion can be maintained during particulate filter regeneration, in some examples. Further still, the particulate filter can be regenerated using techniques most appropriate for the current conditions, and thus, emissions can be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.